1ECE 274 - Digital LogicLecture 22

Lecture 22 Implementation Manufactured IC Technologies

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Full-Custom Integrated Circuit Full-Custom Integrated Circuit

Chip created specifically to implement the transistors of the desired chip Layout detailed description how each transistor and wires should be

layed on a chips surface Typically use CAD tools to convert our circuit design to a custom layout Fabricating an IC is often referred to a silicon spin

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Full-Custom Integrated Circuit Full-Custom Integrated Circuit

Pros Maximum performance

Cons High NRE (Non-Recurring Engineering) cost

Cost of setting of the fabrication of an IC Often exceeds $1 million

May take months before first IC is available

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Semicustom (Application Specific) Integrated Circuits - ASICs

Gate Arrays Utilize a chip whose transistors are pre-designed to forms rows

(arrays) of logic gates on the chip Sometimes referred to as sea-of-gates

Pros Much cheaper than full-custom IC Fabrications time is typically several weeks

Cons Less optimized compared to full-custom IC - Slower performance, bigger

size, and more power consumption

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Semicustom (Application Specific) Integrated Circuits - ASICs

Standard Cells Utilize library of pre-layed-out gates and smaller pieces of logic (cells)

that a designer must instantiate and connect with wires Pros

Can be better optimized than gate-array Longer to design then gate-array

Cons Less optimized compared to full-custom IC Less NRE and fabrication time than full-custom IC More expensive than gate-array

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Semicustom (Application Specific) Integrated Circuits - ASICs

Cell Array Standard cells are replaced on the IC with only the wiring left to be

completed Sometimes referred to as sea of cells

Structured ASIC Popular term describing ASICs whose gates or cells have been

preplaced

7Semicustom (Application Specific) Integrated Circuits - ASICs

Implementing Circuits Using only NAND Gates NAND gate is a universal gate Universal gate Logic gate that can implement any Boolean function

using gates of that one type only

Implementing a NOT gate using a NAND gate

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Semicustom (Application Specific) Integrated Circuits - ASICs

Implementing Circuits Using only NAND Gates Implementing an AND gate using a NAND gate

Implementing an OR gate using a NAND gate

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Semicustom (Application Specific) Integrated Circuits - ASICs

Implementing Circuits Using only NAND Gates Implementing a half-adder using only NAND gates

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Programmable ICs FPGAs Field Programmable Gate Arrays

Prefabricated ICs that contain all of the transistors and wires Designer can program the FPGA to implement our desried circuit

Programming refers to downloading a series of bits to the FPGAs memory Fast - Progamming typically takes seconds to minutes

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FPGAs Field Programmable Gate Arrays

Lookup Tables Memory used to implement a combinational circuit A 1-bit wide memory with N address lines (2N words) can implement

any Boolean combinational function of N variables

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Design Challenge Design Challenge

Draw a circuit using AND, OR and NOT gates for the function F(a,b,c) = abc + abc. Convert that circuit into using NAND gates only.

Due: Next Lecture (Friday, December 2)

Extra Credit (Homework) 2 points